The invention relates to contact lenses. In particular, the invention provides contact lenses that incorporate one or more stabilization zones to stabilize the orientation of the lens in relationship to the eye.
It is known that the correction of certain optical defects can be accomplished by imparting non-spherical corrective characteristics into a contact lens, such as cylindrical or multifocal characteristics. Additionally, advances in technology permit production of lenses customized to a particular wearer using corneal topographic and wave front aberration measurements. The use of these lenses may be problematic in that the lenses need to be maintained at a specific orientation while on the eye to be effective. However, a lens will rotate on the eye due to blinking as well as eyelid and tear fluid movement.
Lenses designed to maintain their on-eye orientation typically are of two general types. One type uses prism stabilization, or thickening of certain lens portions, to maintain orientation. Examples of prism stabilization methods include decentering the front relative to the back lens surface, prismatic balancing, thickening of the lower lens edge, supporting the lens on the lower eyelid, forming depressions or elevations on the lens"" surface, and truncating the lens edge.
A second lens type, dynamically stabilized lenses, uses the movement of the eyelids to maintain lens orientation. Dynamic stabilization methods include reducing the thickness of the lens"" outer surface at two symmetrically lying regions, typically top and bottom zones on the lens, while maintaining the thickness of the outer regions in the horizontal center axis.
The known methods for maintaining lens orientation suffer from a number of disadvantages including that lenses incorporating the methods require specialized, off-axis tooling for production, that these lenses are uncomfortable to wear, and that the known methods are not highly effective. Thus, a need exists for a method of maintaining on-eye orientation of a lens that overcomes some of these disadvantages.